Automatic pilot for aircraft



July 22, 1952 A. P. GLENNY 2,604,074

' AUTOMATIC PILOT FOR AIRCRAFT Filed Marh so, 1948 I Invenlor Hen-10R HJILIP GLENNY Patented July 22, 1952 AUTOMATIC PILOT FOR AIRCRAFT 7 Arthur Philip Glenny, Hanworth; England, as-

signor to The Sperry Corporation, a corporation of Delaware Application March 30, 1 948,'Serial No. 18,0ll4

The present invention relates to improvements in automatic control systems or automatic pilots for controlling a craft to maintain a desired attitude or path and, in particular, to improvements in means for ensuring that an automatic pilot is correctly adjusted before it is put into operational control of the craft.

An automatic pilot controls a craft by actuating a control surface by means of a servo-motor. The servo-motor is caused to move in one direction or the other 'by the supply to it of power under control of a relay, e. g., an electric relay or a valve, which is itself usually controlled by rectly controls the supply of power to the servomotor (and perhaps some preliminary relays that control the final relay) 'is not put into operational control of the servo-motor until after the control arrangements for developing the control quantities are energized, and the source, e. g., a pump or electric generator, from which the servomotor is energized under the control of the final relay, is rendered operative. The final step in the'process of putting the automatic pilot into control of the craft is therefore one in which the final relay, and perhaps also some other relays in the chain of control, is rendered efiective' tocontrol the servomotor.

Should a fault, such as the sticking of a valve or a disconnection in an electric circuit in the apparatus, exist, or should a manual adjustment setinto-the apparatus to develop a signal that will maintain a desired flight condition-of the craft not beappropriate to maintain the existing fiightycondition, the change from manual 'to automatic control may resultin the craft'assuming suddenly a dangerous attitude. The

"principal object of the'invention is to provide,

in an automatic pilot, means for indicating the operational state of the apparatusimmediately before the craft is put-under its control.

According to the invention an automatic control system-is provided ofthe kind in which a signal" or signalsderived from'a reference instrument or instruments controls actuation of. a

5Claims. (01. 121-38)" 1 lies along the longitudinal axis of the craft.; 0n

2i a control surface through a'servo-system that includes a final relay directly controlling operation of a servo-motor actuating the surface, characterized in that a switch device is provided for putting the automatic control system, into control of the craft in two successive stages in the first of which all parts of the system that determine the operation ofthe final relay are rendered operative so that the final relay is actuated but is prevented-from effecting actuation of the servo-motor, while in thesecond stage the final relay is put into operational control' of the servo-motor and in that an indicator is provided for indicating the operational stateof the final relay during the first stage. v

One embodiment of anautomatic control-system according to the invention as appliedfto control the elevator, of an aircraft will nowbe described with reference to the accompanying drawing by way of example. 'i

In the drawing lis'a gyro vertical with-its casing (not shown) mounted" on the craft in such a way that the outer axis of the gyroscope the outer gimbal-frame 2 is fixed the winding 3 of a potentiometer, whose wiper 4 is fixed to g the inner gimbal-frame shaft 5, The en'ds of the winding 3 are connected to slip-rings 6 carried on theshafts l, 'l', of the outer gimbal-frame, the slip-rings co-operating with brushes 8 mounted on the gyro-vertical casing and connected to the ends of the winding 9 of a second potentiometer mounted on the craft and provided with a manually adjustable wiper Ill. The wipers 4. and [0 are connected to the control coil ll carried on the tongue, l5 ofa polarised relay l2. The tongue also carries a second coil 38 connected .to a potentiometer 4| actuatedby servo-motor '24 :to provide a feed-back signal. Potentiometer 4| comprises two resistor coils.39, 39f, energised in parallel, and the mid-point 38 of coil 39'- being connected to one side ofjthe coil 38, and; the wiper 40 to the other side. "The wiper co-operates .with resistor 39 and isactuated by servo-motor 24 A variable resistance 43 is inserted in lead 42 connecting the, potentiometer 4|. to the positive side of the source through a three-position switch ST-to be -described presently. v i g The relay is in the form of'a rectangular frame l3 of'magnetic material with an ,air gap ltwln the bottomside, the tongue 15 being, fixed to a shaft l6 mounted'for angular movement about an axis in the middle of the top side of theframe and perpendicular to. the plane of the frame.

The vertical sides of the frame carry polarising windings l1, [7. Fixed to the shaft I6 is a link l8 connected to the piston I9 of the pneumatic control switch or final relay 20 of known type. The final relay has its inlet port 2| connected to a source of air pressure (not shown) and its outlet ports 22 connected by conduits 23 to the pneumatimiservom'otor 24 -of=known type, and also towthetwo inlet-iports 25 of a:-by-pass valve 26 shown in section in the drawing. Each inlet port of the by-pass valve is connected to :a long narrow outlet port in thediormlnf a slot whose transverse section is shownimthe drawing and which is opened.; ornclosed-g1loya-a asap or slider 29 which moves imazdireetio izpemendicular to the lengths of the slot. The outlet ports are normally maintained openlby thelactionioi a compression spring 30 which pressesthe slider against an arm 3|, pivoted at 32 and;res;tin;g against a stop 33 fixed relatively to the craft. solenoidifl is. arrange drab we the valyenand nattractssansarmatureaM carried. near "the .;top oirlthe arm ,whenaenergized, lthus' moving ,the armiaboutl-theapivot 32.. and 1, moving .the ,.slid er \29:-.:to,.close 1311855101 ports,.,2.'l. Closeltoleachlslot s-andharrangedso. as to,be.subjeicted.to air currents -issuing;therefrom isaresistance'. 34,;3'4' reach: of qwhich formsfonearm of, abolometerib'ridgelacross which.is;connectedia.1arnp"3fi,or.36,' .i Thel'threegpo'sltion switch Q31 sis arranged so that. in I its -iflofl'" ror fiA 'iposition, the, source of eelectrical @ene l y .(notgshown) is disconnected, while, inits i fiesvsor fBsPosition, ,the,p.ositivejsidel oftLthe source;isaconnected byi IeadJA-Z lto ,energise the potentiometer windings 3 ,and;i9;;ir parallelhthe 7 nnqlarising, coilaoiithe relay I]; inseries; the; two lo'olometer ,bridgesfihifl iin parallel ,and the QfinaLIeIay -2Uwto,- a sourceuoflairgpressure linot shown).' .lln the oni or ficfpo'sition; the switch, in addition to maintainingthe connectionsmade lgimthe B;.,-position alsoiconnectsthelsource to sencrg'ise the solenoid]! I .'byl.lea'd"43. I

fllheioperation .of .theapparatus will nowvlibe explained. wwhenuthe switch .31,- Bin ,theiffiiff positionmthe,electrical "circuitsareidisconnected lifr om nthe sourcewand, -lithe .y'alve 22.6;heing ripen,

ruthessrizo -.motor.=-is= ineffective. vOn. ,movingf the aswi tch ato the ites'ti positionithe "electrical, circiiits except ionsolenoid I44, areuconnected to ithis'l'isourceiof ..electri cal energy and i. the final irelayfjni'islconnectedloitso source of; air pres- I .-.;'sure;' by lmeans snot, shown. i In order vthat the iiiiicnof tne craft maynotbe iiisturbedp uttin ILtheaaiflioma'tic "control apparatus in "control of Ithe,craftlthe final relayiiflishould'then becenr. islets I21 ,12 'l ,":iri by-pass *valve 2 -resi'stancesi-s l, j I34'ibeing (at the "same temperature and "the Ybridgesibalanced sotthat the, lamps $6,*-"36-will fiboth' be unlit. If, howeverfidue'tw some" cause 'y'ness'n'frelay valve 2flrarrair current issues from fslotZl, saYJdamprrS lirwilldight up and warn "the 'Ilfilot'ofithe'craftfofthe unsatisfactory state-of fthe; apparatus, in-whi'chcase he will refrain' from puttin'g't the""apparatus into control of the air- 4 to be thrown in and out of use, a master control instrument, a pick-off thereat for generating a control signal of low power, a servo-motor, a normally centralized relay between said instru- 5 ment and motor for actuating the latter, said relay being responsive to said low power signal and including a means for controlling the ap- :;plication of ya ihigher'g power to said motor, a ntwo-stage starting switch-tier putting the pilot into control, the first stage of said switch eniergizing said relay and low power control system,.safety,means for preventing said relay from applying said higher power to said servo-motor, rgandg a 3w!arming;signa1 actuated in case said re- 1;5 'zlayiis-ionzcentralized when energized tending to prevent the starting switch from being moved tolthelsecondl'stage until said relay is centralized.

;':-2.ii'-Irr.=an automatic pilot for aircraft adapted to be thrown in andmut of use, a master conatnoliinstrumenta pickeofisthereatlfor eener is he a econtrol signal a-of low powenl-ia risecon nnanually adiustable picksofh bothppposi g lthe -signal from saidfirst; picksoif,v sservoemotbrs a r normally {centralized relay fbetweengsaid ,instru- -ment ranmotor: for actuating the ,latter said relay being responsivez-to the ;,net gsignal from :said picksofis 1 andincludin Ta .=yalu I for- {controllingthe application of a ,highempower toasaid .;motor,--;saf.e,ty means iorainitiallvipreventing,said ay -:from.-epp1y n said- ,hiaher',p0wert0esaid .-,seryosmotor, .,a warningrsignaln and, rn eansgior abringingisaid-warning signal into operationjwith said rsafety: means, beioreathe pilotr becomesggpas -:.erative;;-ifaany:-net signa1-.i%nresent to-rholds said ,relavoilzits: neutral position. .--3.,In;;an automatic pilot {or-{airman adapte :ZQE' EIJ'I J-ZQWI T'HI andsou ofz seis r mastenccmtrm instrument, saggipickaqff zthereat. iorgsenerat n i a 4n i.-'control zsignalaof lilow powerm a. servo-m tor, a

iollow-baclg,pick-oiliatlsaidi SQIWQflI OtQI, a thir manually adjustable pick.-,Qf ,-1both:oppqsilig the signal; fromnsaidgfirst picks-Of w a normally cen- :tralized relay betweensaidlinstrumentaand motor v sfonactuating thelattersaidr laylbeine respon- 'sive -.to'.'=the ,net f-sienalifrom i said nick.-.01Is.,.and including a ivalve. fforicontrollingsthe, application total-higher ,power. to. :said, ,mot,or,,:; .sai,e tyi .means '..-for initially preventing said relayiromlapplyi l saidshigher -powerto said .=ser,vo,-motor,- .a; warnsmgisignali and means ifor ,brin nsisai r wam- 1..ing signal intoioperationrwi r-fia disa fetyrmfian qbefore theipilot -finally, becomes,opcera ive i any enet sign l is presen rte: rhold the relays-off Exits Ljtralised sojth'at no airlcurrents'shouldissue-from' 555-1131117131: DOSitiOn.

4.,In1 an -.aut0matic;,.pilot ion aircraft. adapted l-to-ber-thrownin and; out of use,-ra imastergcontrol instrument, ,.a:n--;electrical =ipickeoff ,thereat own-generating la,- reversiblasignalfonirelative tilt of the:,craft. and ,-instrument proportional to .the

= tilt, z-a esecondxmanually. adjustable picls ofi fm (modifying said.- (Athens-signal torchangevztherzat- V ti-tude rOf the craft,v an ielectro -fiuid;p1=essure:-1?ei lay controlled by the netgsignalfrom said; pick- 5 cilia-1a ;fi uid pressureiservomontrollemby said ,relay {for :operatin awcontrol .surfacesof, the

craft, a two-stage switch for throwing yin the pilot, .and v:means re sponsive to any unbalance ;.:pressureleading ;1to ,-sa-id:rmotor -,-,from- ,said gep in Y? a "m an preventing-"turning of gth V switch-to its second; position.

15.,-;A- safety; device for airplane automatic pilots ,as ;;claimed .-,in claim -,wh erein asaid --;lgy-

- f" 1. In an automaticaipilot fomaircraftr-adaptedxfimass-means; includes iagrnqrmfiill-y ppen pypass valve in each of the two pressure lines between the relay and motor, means responsive to unequal flow therefrom for causing the pilot to centralize his controls, and means for closing said bypass upon said switch being placed in its 5 second position.

ARTHUR PHILIP GLENNY.

REFERENCES CITED The following references are of record in the 10' file of this patent:

UNITED STATES PATENTS Number Name Date Nicolai Apr. 9, 1912 Roland Apr. 23, 1940 Rosenberger Feb. 20, 1945 Wales Apr. 10, 1945 Frische Apr. 16, 1946 Hansen Feb. 18, 1947 

